When mounting a TXV bulb or checking bulb placement, there are a few important considerations (listed in order of importance):

1. Mount the bulb on the suction line. Flapping in the breeze is no good.
2. Mount it TIGHTLY with a proper metallic strap (usually copper, brass, or stainless steel)—not with zip ties or tape.
3. Position it on a flat, clean, smooth portion of the horizontal suction line—not on a coupling or an elbow.
4. Mount it before the equalizer tube (in other words, put it closer to the evaporator than the EQ tube).
5. When possible, mount it at 8 or 4 o'clock on the suction line (or according to manufacturers' specs). This becomes more important the larger the suction line.
6. When possible, insulate the bulb so that it is not influenced by the ambient air temperature. It never hurts to insulate the bulb, even inside the cabinet, though not all manufacturers require it.
7. If you do need to mount it vertically, make sure the tube points up, not down.

Poor bulb contact will (generally) result in a bulb that is warmer than desired, resulting in overfeeding and lower than desired superheat.

Finally, be gentle with the bulb and tube. They break easily.

You can read a more detailed description HERE.

—Bryan